[wasm] Initial signal handler

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 4e5a7c8fd983d2dfb3c710024ff32c5b63e34baf..40ae9d8ff8e114fbc5beb94c8e7d7ef41b1bbec4 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1203,6 +1203,10 @@ Object* Isolate::UnwindAndFindHandler() {
   for (StackFrameIterator iter(this); !iter.done(); iter.Advance()) {
     StackFrame* frame = iter.frame();
 
+    if (frame->is_wasm() && trap_handler::EnableTrapHandler()) {

[titzer, 2017/01/09 09:26:56]

I think this logic is correct, but maybe it would be more straightforward to
just unconditionally set the ThreadInWasm flag to be true if the handler frame
is wasm, and false otherwise?

[Eric Holk, 2017/01/10 23:10:48]

Was the concern about the extra call to EnableTrapHandler()? If so, I went ahead
and removed that.

Otherwise, we want to clear the ThreadInWasm flag when we unwind out of a Wasm
frame, which is what's happening here.

+      trap_handler::ClearThreadInWasm();
+    }
+
     // For JSEntryStub frames we always have a handler.
     if (frame->is_entry() || frame->is_entry_construct()) {
       StackHandler* handler = frame->top_handler();
@@ -1234,6 +1238,13 @@ Object* Isolate::UnwindAndFindHandler() {
 
           handler_sp = return_sp;
           handler_fp = frame->fp();
+
+          // This is going to be handled by Wasm, so we need to set the TLS flag
+          // again.
+          if (trap_handler::EnableTrapHandler()) {
+            trap_handler::SetThreadInWasm();
+          }
+
           break;
         }
       }